Judicial administration of justice through reasoned interpretation, application and clarification of legal principles and rules is among the oldest paradigms of constitutional justice. The principles of procedural justice underlying investor-state arbitration remain controversial, especially if confidentiality and party autonomy governing commercial arbitration risk neglecting adversely affected third parties and public interests. There are also concerns that rule-following and formal equality of foreign investors and home states may not ensure substantive justice in the settlement of investment disputes unless arbitrators and courts take more seriously their customary law obligation of settling disputes in conformity with human rights obligations of governments and other principles of justice calling for judicial balancing of all private and public interests affected by the dispute. The constitutional task of judges to apply the law and settle disputes in conformity with principles of justice may require reviewing whether judicial reasoning remains compatible with redistributive principles of case-specific equity, social justice and corrective justice.